I spent a night at central hostel Florence along with a friend. We had made an online booking in a 5 bed dorm, so upon arrival we were handed the keys and a map of Florence. The room was ok, not something really special but not bad either. The bathroom, which was shared among a couple of dorms was acceptably clean, though it could have been a bit cleaner. Overall, it was a pleasant experience.
The hostel has a courtyard with tables and chairs where it is possible to sit and socialize with the rest of the visitors. It also offers free linen, which is definitely a plus. However, its best feature is its location. It is really close to the train station (Firenze S.M.N) and to the city centre with all the main sights and right next to a supermarket.
You may find the numbering of the buildings rather confusing, but you can just ask, the locals can help you with that.
As a disadvantage, I would mention that the owner does not speak English, which can make the communication part rather confusing, but this is quite common in Italy, so you should be prepared anyway!
Summarizing, Central hostel Florence was quite cheap, acceptably clean and really conveniently located. If you do not speak italian some communication problems are possible, but I would generally recommend it.